Document FR-A-2 772 319 describes an example of such a vehicle seat in which the seat proper is pivotally mounted, substantially in the middle of its two side faces, on the first connecting rod, and, when in the deployed position, is blocked on the bottom portion of the seat back. To do this, the rear portion of the seat proper includes a cross-member that is kept engaged in a hook disposed in the bottom portion of the seat back.
To go from one position to the other, that type of seat requires two distinct operations to be performed, comprising both positioning the seat back, and also blocking or unblocking the seat proper in the seat back.